Multi-passage electron multiplier with potential differences between passageways



June 4, 1968 J. ADAMS 3,387,137

MULTI-PASSAGE ELECTRON MULTIPLIER WITH POTENTIAL DIFFERENCES BETWEEN PASSAGEWAYS Filed April 29, 1964 3 8 FIG! FIG.3 PRIOR ART 9 8 2 QVZ'ZflOfifiUfi 1 I I I I I I I I 13 10 ,26

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ELECTRIC FIELD LINES AGENT United States Patent 3,387,137 MULTI-PASSAGE ELECTRON MULTIPLIER WITH POTENTIAL DIFFERENCES BETWEEN PASSAGEWAYS John Adams, East Grinstead, England, assignor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Apr. 29, 1964, Ser. No. 363,496 Claims priority, application Great Britain, May 1, 1963, 17,280/ 63 3 Claims. (Cl. 250-213) ABSTRACT OF THE DISCLOSURE An image intensifier employing a multi-passage electron multiplier between a photocathode and a fluorescent screen. Alternate conductive strips on opposite faces of the electron multiplier are maintained at different potentials so that an electrical field can be maintained in the passages of the electron multiplier support, the lines of force of which field extend obliquely to the axes of these passages.

In electron-optical image intensifiers use may be made of secondary-emission multiplication of the initially fairly weak flow of electrons obtained by photo-emission. Secondary-emission multipliers are known; they comprise a great number of parallel passage ways, for example tubular channels in a thin plate of insulating material, which is arranged transversely of the direction of travel of the electrons. The two faces where the passage Ways open out, are coated with a metal layer, to which supply condoctors are connected for the application of an electric voltage which accelerates the electrons.

The perforated plate may be made of insulating material. In this case the walls of the channels are coated with a thin layer of resistive material. The required electrical conductivity for a uniform distribution of the voltage along the surface may also be obtained by using certain kinds of glass having a reduced internal resistance.

When the material used for the manufacture of the perf-orated plate does not contribute to. an increase in the flow of electrons by secondary emission, the passages must be coated with secondary-emissive material.

The coincidence of the direction of propagation of the electrons with the axes of the channels brings aboutthat electrons covering paths parallel to the direction of propagation from the input side to the output side of the channels do not take part in the electron multiplication. The intensification obtained is therefore less great and it may furthermore be non-uniform for image points having relatively different electron densities, while the stray of the electron paths is not the same anywhere.

The invention has for its object to avoid said disadvantages and relates to an electron-optical image intensifier with a secondary-emission multiplier consisting of an assembly of closely adjacent, narrow passages in a support having parallel faces coated with a metal layer, where the passages open out, while the walls of the passages have slightly electrically conducting faces of satisfactory secondary-emissive properties. In accordance with the invention the conducting coating on at least one of the two faces of the support consists of narrow, parallel strips which extend in the direction of one dimension of the face throughout the length thereof and in the direction of the other dimension are separated from each other, while the strips are alternately connected electrically to each other and to supply conductors for the connection to a voltage source.

The conducting coatings on both sides of the secondary- 3,387,137 Patented June 4, 1968 "ice emission multiplier preferably consist of separate, parallel strips. Under the action of voltage-s applied to the strips, an electrical field can be maintained between the two faces on either side of the support, the lines of force of which field extend obliquely to the axes of the passages. Electrons entering the passages on one side are guided by said field in paths terminating at the walls of the passages. The electrons travel under the action of the field components parallel and normal to the axes of the passages in wave-shaped paths along a narrow strip of the wall surfaces of the passages. By controlling the voltages, the intensity of the field and the deviation from the direction of propagation can be adjusted, so that both the image intensification and the most favour-able contrast ratio can be adjusted.

The invention will be described more fully with reference to the drawing, in which FIG. 1 shows diagrammatically an image' intensifier with an electron multiplier,

FIG. 2. shows a small part of the electron multiplier in a sectional view,

FIG. 3 shows an embodiment in a side elevation, and

FIG. 4 shows in more detail an end view of the electron multiplier.

The electron image tube comprises an exhausted envelope 1 and a photo-electric cathode 2 and a luminescent screen 3. By means of the lens 4 a projection of the object 5 is produced on the photo-cathode 2 and a luminescent image is produced on the phosphor screen 3, said image corresponding to the photo-cathode image and being observable from the spot 6.

Between the photo-cathode 2 and the luminescent screen 3 there is arranged the secondary-emission multiplier 7. In principle, it is formed by a very great number of narrow passages 8 in a plate of insulating material or of material of low conductivity 9. The pass-ages 8 communicate with the left-hand side and the right-hand side of the plate, both sides being coated with conductive material. A thin aluminum layer applied by spraying constitutes a good conductor. In this case the layers are not homogeneous, but they are formed by strips so that the coatings 10 of a number of dams between the passageson one side are electrically separated from the coatings 11 on each intermediate dam (see FIG. 4). On the opposite sides the strips 12 are electrically separated from the strips 13. The four groups of strips are provided with voltage contacts 15, 1'6, 17, and 18. By these contacts the coatings are connected to different points of a number of voltage sources. The contact 15 has the lowest potential. The contact 16 derives an adjustable voltage from the voltage source 19 of for example 50 v.+. Between the contact 16 and the contact 17 of a set of strips on the other side of the multiplier there prevails a high positive voltage of for example 5000 v., which is supplied by the voltage source 20 and the contact 18 derives a voltage of a value for example 50 V. higher from the voltage source 21. The two contacts 16 and 18 can be displaced in common and are therefore coupled with each other by a line 22. The voltage source 23 is connected in series with the said sources 19, 20 and 21 and is connected to the l-u minescent screen 3. Electrons emanating from the photocathode along the paths 2-4 and entering the passages 8 travel along curved paths 25 and strike repeatedly the walls of the passages which are secondary emissive, i.e., they may be provided with a layer 30 of secondary emissive material. Each impact is attended with the release of a number of secondary electrons, so that the intensity of the flow of electrons increases after each impact. The emerging electrons 26 strike the luminescent screen 3.

The paths covered 'by the electrons are formed under the action of the electrical fieldbetween the two faces of the multiplier. When the strips 10 and 11 on one side have equal potentials and also the strips 12, 13cm theother side, the lines of force of the electrical field are parallel to the passages. By raising the potentials of the strips 10 on one side and of the strips 12 on the other side, a transverse component is added to the electrical longitudinal field in the passages 8, which component gives rise to an oblique direction of the field lines with respect to the passages. Such lines 27, 28 are indicated diagramatically and the lines 27 extend obliquely in every other passage in one direction and the lines 28 extend in the opposite sense in the intermediate passages. In one set of passages the electrons travel along the lower side of the Wall and in the other set of passages along the upper side of the wall. The number of impact places may be varied by increasing or decreasing the voltage differences between the strips. A suitable combination of voltages is given by way of example in the following table.

V. Photocathode 200 Conducting strips 10 0 Conducting strips 11 +50 Conducting strips 13 +5000 Conducting strips 12 +5050 By a variation of the voltages across the strips 11 and 12 the angle 0: indicating the slope of the lines of force varies.

The passages 8 may be arranged in a uniform pattern of orthogonal lines, while between the openings of the faces are coated with conducting strips 10 and 11 (see FIG. 4).

What is claimed is:

1. In an electron-optical image intensifier including a photoelectric cathode and fluorescent screen positioned on opposite sides of a secondary emission electron multiplier wherein said multiplier comprises an insulating block having a plurality of parallel, closely adjacent narrow passageways therein opening out on opposite faces of said block perpendicular to said cathode and said screen, the walls of said passageways having slightly electrically conducting and secondary emissive surfaces, a conductive coating on the surfaces of said block on which the passageways open out, said conductive coating comprising a plurality of narrow, parallel strips which extend in the direction of one dimension of said surface through the length thereof and are separated from each other in the transverse direction, means to connect alternate strips on each surface together and to different potential sources maintaining a potential difference therebetween whereby an electrical field can be maintained between the opposite faces on either side of the insulating block the lines of force of which field extend obliquely to the axes of the passageways, and adjustable means for controlling the potentials applied to said strips whereby the intensity of the field and deviation from the direction of propagation of electrons can be adjusted and thereby a favorable image intensification and contrast ratio can be obtained.

2. An image intensifier as claimed in claim 1, in which both faces of the block are coated with a metal layer consisting of separate strips, Whilst every other strip on one side has the same potential, said potentials differing from each other and the potential differences of opposite strips on either side are the same.

3. An image intensifier as claimed in claim 2, which includes means to adjust the potential differences of the strips on one face and the potential differences between the strips on the other face of the block in common.

References Cited UNITED STATES PATENTS 7/1958 Wiley 3l3l04 2/1966 Goodrich et a1 250-207 X 

